Nucleotides and nucleic acids

• • Gene's role in determining amino acid sequence: Base triplets code for specific amino acids
  • DNA purification by precipitation: Add ethanol & salt, centrifuge to obtain nucleic acid pellet
  • Transcription: Produces mRNA in the nucleus, RNA polymerase binds to gene's promoter region, free nucleotides attracted to complementary bases, phosphodiester bonds formed
  • After mRNA transcription: RNA polymerase detaches, H-bonds reform, DNA rewinds, splicing removes introns, mRNA moves to ribosome
• • Complementary base pairs in DNA and RNA: DNA - 2 H-bonds between A+T, 3 H-bonds between G+C, RNA - 2 H-bonds between A+U, 3 H-bonds between G+C
  • DNA replication: Semiconservative replication, old strands act as templates, new DNA contains 1 old and 1 new strand
  • Role of DNA helicase in replication: Breaks H-bonds between base pairs to form single strands
  • Formation of new strand in replication: Free nucleotides attach to exposed bases, DNA polymerase joins nucleotides in a 5’ → 3’ direction, H-bonds reform
  • Features of genetic code: Non-overlapping, degenerate, universal
• Nucleotides and nucleic acids:

  • Nucleotide structure
  • Pentose sugars in DNA & RNA: DNA - deoxyribose, RNA - ribose
  • Formation and breakdown of polynucleotide strands: Condensation reactions form phosphodiester bonds, hydrolysis reactions break these bonds
  • DNA structure: Double helix of 2 deoxyribose polynucleotide strands, H-bonds between complementary base pairs (AT & GC)
  • Purine bases: Adenine (C5H5N5), Guanine (C5H5N5O), two-ring molecules
  • Pyrimidine bases: Thymine (C5H6N2O2), Cytosine (C4H5N3O), Uracil (C4H4N2O2), one-ring molecules
• • Translation: Produces proteins in cytoplasm on ribosomes, ribosome moves along mRNA, tRNA anticodon attaches to mRNA, peptide bonds form between amino acids on tRNA
  • ATP and ADP structure: ATP has 3 phosphate groups, ADP has 2
  • Mutation: Alteration to DNA base sequence, often arises during DNA replication